In recent years, with increase in demand for reducing expenses or time for business trips, transmission systems such as teleconference systems for performing a teleconference over a communication network such as the Internet have been widespread. In such transmission systems, a teleconference can be realized by transmitting and receiving image data and audio data between a plurality of transmission terminals. With recent advances in broadband environment, it is possible to transmit and receive image data of high image quality and audio data of high audio quality. Therefore, it is possible to easily recognize states of other persons in a teleconference, enabling to enhance conversational communications.
In recent transmission systems, relay apparatuses that relay image data and audio data between transmission terminals such as teleconference terminals are installed for each LAN (Local Area Network) in a communication network. These relay apparatuses can reduce loads on each relay apparatus by distributing communication processing for a teleconference, and can distribute data transmission amounts of image data and audio data to be relayed.
Conventionally, when one relay apparatus is selected for use from a plurality of relay apparatuses, a relay apparatus is generally used that is connected to the same LAN as teleconference terminals that perform a teleconference. More specifically, by selecting a relay apparatus with an IP address close to the IP addresses of the transmission terminals, it is possible to transmit and receive image data of high image quality and audio data of high audio quality via the selected relay apparatus (see Japanese Patent Application Laid-open No. 2008-227577).
Conventionally, when a video signal is transmitted to a destination terminal, the video signal is encoded into data for a base layer and data for an enhancement layer; and each data is transmitted by different channels via a relay server. In this case, the data for the base layer is transmitted by a high-reliable channel and the data for the enhancement layer is transmitted by a low-reliable channel. Therefore, even when the data for the enhancement layer cannot be transmitted, the destination terminal can reproduce video by using the data for the base layer (see Japanese Patent Application Laid-open No. 2009-508454).
However, in the teleconference systems, when a relay apparatus with an IP address close to IP addresses of teleconference terminals is used, loads may be concentrated on a specific relay apparatus depending on communication states. More specifically, when use frequency of a teleconference terminal in a local area in the network increases, use frequency of a relay apparatus installed in the same area increases. When a load applied to the relay apparatus exceeds an allowable amount, a failure occurs in the relay apparatus and image data and audio data cannot be transmitted and received, which is a problem.
Conventionally, it is necessary to use a specific relay server for transmitting data for a base layer and data for an enhancement layer, which are communicated between a plurality of terminals. That is, the amount of data to be processed by a specific relay server extremely increases. Therefore, when a load applied to the relay server exceeds an allowable amount, a failure occurs in the relay server, and image data and audio data cannot be transmitted and received, which is a problem.